A rectangular tank measuring 70 cm by 51 cm by 28 cm was to be filled with water by two taps, D and E. Tap D which fills the tank at a rate of 9 ℓ per minute was first turned on for 4 minutes before Tap E was turned on as well. If the tank was filled to the brim in a total of 7 minutes from the time when Tap D was first turned on, what is the rate at which Tap E fills the tank? Give your answer in ℓ per minute correct to 1 decimal place.
Total volume of the tank
= 70 x 51 x 28
= 99960 cm
3 1 ℓ = 1000 cm
3 9 ℓ = 9000 cm
3 Volume of water filled by Tap D
= 9000 x 7
= 63000 cm
3 Volume of water filled by Tap E
= 99960 - 63000
= 36960 cm
3 Rate in which Tap E fills the tank
= 36960 ÷ 3
= 12320 cm3/min
12320 mℓ/min
= 12.32 ℓ/min
≈ 12.3 ℓ/min (Correct to 1 decimal place)
Answer(s): 12.3 ℓ/min